Abstract: Effective stiffness and yield surface of Kagome latticestructure are investigated in the paper. The shape function of singularyield surface is a convex domain in the plane enclosed within four straightlines. The plastic zone of crack tips of mode I and mode II cracks in theinfinite half plane are estimated with the singular yield surface andvalidated with finite element simulation, which are more precise than thosewith Mises smooth yield surface. Thus Kagome could be simplified asisotropic continuum only in elastic deformation; meanwhile, in the case ofmaterial yielding or the strong singular stress field, the strength ofKagome lattice depends on the direction of principal stress.